Lead storage battery

ABSTRACT

The present invention relates to a lead-acid battery Comprising a positive and a negative electrode, each having a current collector comprising an expanded grid, characterized in that at least one of the positive electrode and the negative electrode contains an organic binder in an active material layer at an edge portion thereof.  
     This makes it possible to suppress an internal short circuit resulting from the separation or abnormal growth of an active material due to repeated charge/discharge, thereby remarkably prolonging the cycle life of a lead-acid battery.

TECHNICAL FIELD

[0001] The present invention relates to a lead-acid battery comprisingan electrode using an expanded grid as a current collector. The presentinvention further relates to suppressing an internal short circuitresulting from the separation or abnormal growth of an active material,thereby prolonging the cycle life of a lead-acid battery.

BACKGROUND ART

[0002] In order to obtain a higher capacity lead-acid battery and tofacilitate the production process of the lead-acid battery, an expandedgrid is mostly used these days because an expanded grid can be madethinner than a conventional grid obtained by casting and it can beserially produced.

[0003] In a lead-acid battery, the volume change of the active materialduring charging/discharging is relatively large. Accordingly, therepetition of charging and discharging weakens the binding force withinthe active material, making it easier for the active material toseparate from the electrode.

[0004] In the case where the current collector is a casting grid, it iseasy to form a rigid frame around the electrode. The volume change ofthe active material can be suppressed to a certain degree by filling theinside of the frame with an active material; accordingly, the separationof the active material can be prevented.

[0005] In the case where the current collector is an expanded grid, onthe other hand, unlike the case of a casting grid, it is difficult toform a frame around the electrode because of its production method.Therefore, the active material filling the grid at the right and leftedge portions of the electrode is not surrounded by a frame. As shown inFIGS. 1 and 2 which will be used in examples described hereinafter, in anegative electrode 5 comprising an expanded grid 1 and an activematerial layer 2, the active material layer 2 is exposed outside at theright and left portions of the electrode. Thus, the active material atthese portions of the electrode is likely to separate from the electrodedue to the volume change of the active material duringcharging/discharging. The separated active material deposits on thelower portion of the electrode, which is a cause of short circuitbetween the positive and negative electrodes. This internal shortcircuit degrades the battery characteristics.

[0006] In a valve regulated lead-acid battery, there are cases where theactive material grows abnormally at the right and left edge portions ofthe negative electrode during the repetition of charging anddischarging. The problem arises that the active material grows andreaches the positive electrode, causing an internal short circuit.

[0007] A valve regulated lead-acid battery has a system of reducing anoxygen gas generated at the positive electrode into water at thenegative electrode during charging, which prevents the electrolyte fromgoing away outside the system. This system is a cause of the abnormalgrowth of the active material.

[0008] First, oxygen gas generated at the positive electrode reaches thesurface of the negative electrode and is reduced to water by metalliclead of the negative electrode. Meanwhile, the metallic lead of thenegative electrode which has reduced the oxygen gas is oxidized to alead oxide. Subsequently, the lead oxide is dissolved in the electrolyteand is reacted with sulfuric acid to give lead sulfate. The lead sulfateis reduced to metallic lead by receiving electrons at the negativeelectrode.

[0009] When the oxygen gas is reduced, metallic lead is required to havea solid-gaseous interface because metallic lead causes solid-gaseousphase reaction with the oxygen gas. Further, the produced lead oxide isreduced to lead sulfate and then to metallic lead; thereby, it ispossible to continuously cause the reduction reaction with the oxygengas. Accordingly, it is of importance that the metallic lead also has asolid-liquid interface.

[0010] In view of the above, it is considered that the area where theoxygen gas is efficiently reduced into water is the right and left edgeportions of the negative electrode having larger three-phase interfaces(solid, liquid, gas). Accordingly, an apparent charge and dischargereaction occurs more at the right and left edge portions of the negativeelectrode than other portions; inevitably, the volume change of theactive material is significant at the edge portions, making it easierfor the active material to separate.

[0011] Moreover, since the reduction reaction of the oxygen gas is areaction that accompanies dissolution and deposition, the shape of theactive material changes significantly. Therefore, the abnormal growth ofmetallic lead is likely to occur at the right and left edge portions ofthe negative electrode.

[0012] In order to solve the above problems, for example, JapanesePatent No. 2742804 proposes a method in which a positive electrode plateis encased in a bag-shaped or U-shaped mat separator composed mainly ofglass fiber and a negative electrode plate is encased in a bag-shapedseparator made of polymer resin.

[0013] Further, Japanese Patent No. 3146438 proposes a method to preventthe separation of an active material and an internal short circuit byfilling the space between positive and negative electrode plates and theperiphery of the electrode plates with powdered silica.

[0014] According to the method described in Japanese Patent No. 2742804,a separated active material can be maintained at a certain position, andan internal short circuit resulting from the separation of an activematerial can be sufficiently prevented. However, in order to ensure themechanical strength of a separator made of polymer resin in the processto form the separator into a bag shape, the separator is required tohave a certain thickness. If such separator made of polymer resin isinterposed between the positive electrode and the negative electrode,the space between the positive electrode and the negative electrode willbe widened. This increases the resistance of electrolyte, which degradesthe output characteristics of the battery. What is worse is that thismethod cannot prevent the separation of the active material itself.Thus, as charging and discharging are repeated, the amount of the activematerial not involved in charging and discharging increases, whichdecreases the battery capacity.

[0015] Moreover, according to a method described in Japanese Patent No.3146438, it is difficult to efficiently fill a battery container withpowdered silica, and a significant effect cannot be expected. What isworse is that the permeation of an oxygen gas or the like generatedduring charging is inhibited. Therfore, it is possible that thereduction reaction of an oxygen gas is inhibited, which causes theelectrolyte depletion.

[0016] Furthermore, since the above two methods use a large amount ofpolymer resin or powdered silica which is not involved incharging/discharging, the space equal to the volume of polymer resin orpowdered silica is wasteful and the amount of the active material usefulfor charging/discharging is reduced.

[0017] In order to solve the above problem, it is an object of thepresent invention to suppress an internal short circuit resulting fromthe separation or abnormal growth of an active material, therebyproviding a lead-acid battery with longer life.

DISCLOSURE OF INVENTION

[0018] The present invention relates to a lead-acid battery comprising apositive electrode and a negative electrode, each having a currentcollector comprising an expanded grid, characterized in that at leastone of the positive electrode and the negative electrode contains anorganic binder in an active material layer at an edge portion thereof.

[0019] The organic binder preferably has resistance to acids.

[0020] The organic binder preferably has resistance to acids and theability to form a film.

[0021] The organic binder preferably comprises a resin containing butylrubber.

[0022] The butyl rubber preferably contains butyl isocyanate.

[0023] The organic binder preferably comprises butyl rubber and styrenerubber.

[0024] The present invention further relates to a lead-acid batterycomprising a positive electrode and a negative electrode, each having acurrent collector comprising an expanded grid, characterized in that atleast one of the positive electrode and the negative electrode has aporous resin layer formed on the surface of an active material layer atan edge portion thereof.

[0025] The porous resin layer preferably comprises butyl rubber.

[0026] The butyl rubber preferably contains butyl isocyanate.

[0027] The porous resin layer preferably comprises butyl rubber andstyrene rubber.

BRIEF DESCRIPTION OF DRAWINGS

[0028]FIG. 1 is a perspective view of a (conventional) negativeelectrode before impregnation of an organic binder.

[0029]FIG. 2 is an enlarged perspective view of the portion “X” shown inFIG. 1.

[0030]FIG. 3 is a perspective view of a negative electrode with anorganic binder impregnated therein.

[0031]FIG. 4 is a transverse sectional view of a relevant part of alead-acid battery of Example 1 of the present invention.

[0032]FIG. 5 is a graph showing the relation between the dischargecapacity and the cycle number of lead-acid batteries of Examples 1 and 2of the present invention and Comparative Examples 1 and 2.

[0033]FIG. 6 is a transverse sectional view of a relevant part of alead-acid battery of Example 3 of the present invention.

[0034]FIG. 7 is a graph showing the relation between the dischargecapacity and the cycle number of lead-acid batteries of Examples 3 and 4of the present invention and Comparative Examples 1 and 2.

[0035]FIG. 8 is a graph showing the relation between the dischargecurrent and the discharge capacity of lead-acid batteries of Examples 3and 4 of the present invention and Comparative Examples 1 and 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0036] The present invention is a lead-acid battery comprising apositive electrode and a negative electrode, each having a currentcollector comprising an expanded grid, characterized in that at leastone of the positive electrode and the negative electrode contains anorganic binder in an active material layer at an edge portion thereof.

[0037] Herein, FIG. 1 is a perspective view of a conventional negativeelectrode. As shown in FIG. 1, the conventional negative electrodecomprises an expanded grid 1 with a lug portion 1 a and an activematerial layer 2 filling the expanded grid 1. On each side face of thenegative electrode is attached a sheet of paste paper 3. FIG. 2 is anenlarged view of the portion “X” shown in FIG. 1. The conventionalnegative electrode has the problem that an active material couldseparate from the edge portion 4 thereof because the expanded grid 1 isnot surrounded by a frame and the active material layer 2 is exposed atthe edge portion 4, as is apparent from FIGS. 1 and 2.

[0038] Accordingly, the present invention is characterized in that theedge portion 4 of the active material layer 2, which is exposed becauseof the absence of a frame at the edge of the expanded grid 1, containsan organic binder, as shown in FIG. 3.

[0039] It should be noted that the organic binder in accordance with thepresent invention is a material with binding property comprising atleast one organic compound, or a binder comprising at least one organiccompound.

[0040] The separation of the active material can be prevented since theorganic binder contained in the active material layer at the edgeportion of the electrode maintains its binding force within the activematerial whose volume changes during charging/discharging. It ispreferred that the lower edge portion also contains the organic binderin order to insulate the electrode from separated active material.

[0041] Additionally, the above-described effect can be achieved if atleast, the periphery of the surface of the active material layer at theedge portion of the electrode contains the organic binder. It is morepreferred that the whole active material layer contains the organicbinder because that can further strengthen the binding force within theactive material.

[0042] It is also preferred that the organic binder has resistance toacids. When the organic binder is used in a lead-acid battery, stablebinding force can be maintained for a long period of time.

[0043] It is further preferred that the organic binder has the abilityto form a film. Covering the active material with a much less reactivefilm suppresses the charging/discharging reaction at the coveredportion. This reduces the volume change of the active material resultingfrom the charging/discharging reaction, making it easy to maintain thebinding force within the active material.

[0044] The organic binder film may be formed not only on the surface ofthe active material at the edge portion of the electrode, but also onthe expanded grid itself. In such a case, the effect of insulating theelectrode from separated active material enhances.

[0045] It is preferred that the above-mentioned organic binder comprisesa resin containing butyl rubber. Since butyl rubber is tough andflexible, it is easy to maintain the binding force even if the volume ofthe active material changes.

[0046] The components of butyl rubber include isobutylene and butylisocyanate, etc. They may be used singly or in combination. Among them,butyl isocyanate is more preferred. Butyl isocyanate forms athree-dimensional crosslinked structure by a urea bonding and a biuretbonding; thereby, a tough and flexible resin can be formed.

[0047] It is also possible to further increase flexibility and toughnessby mixing butyl rubber and styrene rubber.

[0048] Although toluene is typically used as the solvent dissolving themixture of butyl rubber and styrene rubber, the use of xylene or othersolvent capable of dissolving the aforesaid organic binder componentsgives a similar result. The use of their mixture also gives a similarresult.

[0049] Further, the present invention is related to a lead-acid batterycomprising a positive electrode and a negative electrode, each having acurrent collector comprising an expanded grid, characterized in that atleast one of the positive electrode and the negative electrode has aporous resin layer formed on the surface of an active material layer atan edge portion thereof. There is no need to mention that the porousresin layer may cover the edge of the expanded grid.

[0050] The porous resin layer maintains the binding force within theactive material of the electrode at the edge portion thereof; thereby,the separation of the active material can be prevented and the internalshort circuit which occurs due to separated active material can beprevented. Herein, the porous resin layer is a porous body with throughholes. Thus, it enables the permeation of oxygen gas generated duringcharging without impeding the diffusion of electrolyte; furthermore, thediffusion of oxygen gas is not impeded.

[0051] A similar effect can be obtained even when the porous resin layerhaving through holes covers not only the surface of the active materiallayer but also the periphery of the surface of the active materiallayer.

[0052] It is preferred that the porous resin layer comprises butylrubber. Since butyl rubber is superior in resistance to acids, theinitial performance can be maintained for a long period of time.

[0053] It is preferred that the butyl rubber contains butyl isocyanate.Since butyl isocyanate forms a three-dimentional crosslinked structurewhen it is cured, the active material can be securely retained. Further,since butyl isocyanate is superior in resistance to acids, the effectcan last for a long time.

[0054] It is preferred that the porous resin layer comprises the mixtureof butyl rubber and styrene rubber. Because the use of the mixtureincreases the flexibility compared to the case of using butyl rubberonly, it is possible to respond more flexibly to the volume change ofthe active material.

[0055] The porous layer in the porous resin layer can be formed by usinga foaming agent.

[0056] In the case where a thermal decomposition type foaming agent isadded to butyl rubber, for example, part of the component obtained bydecomposition during heating of a thermal decomposition type foamingagent supports the three-dimensional crosslinked structure of the butylrubber. The remaining of the decomposed component includes a gas and apolymeric residue. Foam is formed within the resin layer by the gascomponent, and the foam is connected to form through holes. Afterthrough holes are formed, the gas generated is removed with the solvent.Accordingly, the gas hardly remains in the porous resin layer as animpurity.

[0057] On the other hand, although the polymeric residue remains in theresin layer, there is a method to effectively employ it. For example,when hydrophilicity is imparted to the porous resin layer, a foamingagent for allowing sulfone group to remain as a residual substituentshould be selected.

[0058] Preferred thermal decomposition type foaming agent includeazodicarbonamide, dinitrosopenta-methylene-tetramine, 4,4′-oxybisbenzene sulfonyl hydrazide, etc. There are many other foaming agentswhich have different foaming temperature and different decomposedproducts because of the differences in structure, molecular weight,substituent, etc. Accordingly, it is possible to adjust the porosity,diameter, thickness and size of resin skeleton of the porous resinlayer. They can be used optionally according to the purpose, or they canbe used in combination of two or more.

[0059] The porosity of the porous resin layer can be set freely byselecting the type of foaming agent, controlling the added amount, etc.Preferably, the porous resin layer has a porosity of 30 to 90%. When theporosity exceeds 90%, the diffusion of the electrolyte or the permeationof the oxygen gas during charging/discharging is not be inhibited, butthere is a possibility that an internal short circuit occurs because theactive material reaches the counter electrode via through holes.

[0060] Conversely, when the porosity is less than 30%, the number ofthrough holes is reduced, inhibiting the diffusion of the electrolyte orthe permeation of the oxygen gas.

[0061] In the following, examples of the present invention are explainedin detail. It is to be understood that the present invention is notlimited to the examples. Although the examples of the present inventionuse valve regulated lead-acid batteries, it has been confirmed that theuse of a flooded lead-acid battery also gives a good result.

EXAMPLE 1

[0062] (i) Production of Negative Electrode

[0063] Slits were made in a lead-tin-calcium alloy sheet consisting of0.08 wt % of calcium, 0.8 wt % of tin and the rest amount of lead, whichwas then expanded to form squares. Thereby, an expanded grid 1 with alug portion 1 a was produced.

[0064] A negative electrode paste was prepared by mixing powdered lead,water, sulfuric acid with a specific gravity of 1.41, powdered carbon(DENKA BLACK), barium sulfate, a lignin derivative and polyester staplefiber at a weight ratio of 1000:115:70:4.1:21:4.1:1, followed bykneading.

[0065] The above-obtained expanded grid 1 was filled with the negativeelectrode paste to form an active material layer 2. Then, a sheet ofpaste paper 3 made of kraft pulp and reinforcement for preventing theseparation of the active material was attached to each side face of theelectrode, which was then cured and dried to give a negative electrode 5as shown in FIGS. 1 and 2.

[0066] (ii) Addition of Organic Binder to Active Material Layer at theRight and Left Edge Portions of Negative Electrode

[0067] Butyl rubber and styrene rubber were mixed at a weight ratio of97:3. A resin solution was prepared by dissolving 30 parts by weight ofthe obtained mixed resin in 70 parts by weight of toluene. The right andleft edge portions 4 of the negative electrode 5 were respectivelyimmersed in the resin solution. After the active material layer 2 at theedge portion 4 of the negative electrode 5 was impregnated with theresin solution, it was dried at 120% to remove toluene. During drying,the organic binder comprising butyl rubber and styrene rubber permeatedthrough the active material layer 2 at the right and left edge portionsof the negative electrode 5, and the surface of the active materiallayer 2 was covered with a film of the organic binder. FIG. 3 shows thenegative electrode after impregnation of the organic binder.

[0068] (iii) Production of Positive Electrode

[0069] Slits were made in a lead-tin-calcium alloy sheet consisting of0.08 wt % of calcium, 1.2 wt % of tin and the rest amount of lead, whichwas then expanded to form squares. Thereby, an expanded grid wasproduced.

[0070] A positive electrode paste was prepared by mixing powdered lead,water, sulfuric acid with a specific gravity of 1.41, tin sulfate(SnSO₄) and polyester staple fiber with a length of 2 mm and a diameterof 10 μm at a weight ratio of 1000:115:70:10:1, followed by kneading.

[0071] The above-obtained expanded grid 6 was filled with the positiveelectrode paste. Then, a sheet of paste paper made of kraft pulp andreinforcement for preventing the separation of the active material wasattached to each side face of the electrode, which was then cured anddried to give a positive electrode 8.

[0072] (iv) Assembly of Lead-Acid Battery

[0073] There were prepared twelve positive electrodes 8 obtained in theabove, thirteen organic binder imparted negative electrodes 5 and twelveglass mat separators 9 obtained by forming glass fiber with a diameterof 3 to 5 μm and one with a diameter of 0.5 to 1.0 μm into a sheet. Theaforesaid separator 9 was folded in half and the positive electrode 8was encased in the folded separator, which was then stacked alternatelywith the negative electrode. FIG. 4 shows a sectional view of a part ofthe stack. A strap for collecting currents was formed on the stack bycasting to give an electrode assembly. This electrode assembly wasinserted into a battery container, and the strap was resistance-weldedto connect cells. Then, a battery container lid was provided. Dilutesulfuric acid electrolyte solution with a specific gravity of 1.30containing 10 g/L of sodium sulfate was poured into the batterycontainer, and a safety valve was provided to obtain a sealed lead-acidbattery with a rated voltage of 12 V and a nominal capacity of 65 Ah.This battery was referred to as Battery A.

EXAMPLE 2

[0074] A sealed lead-acid battery with a rated voltage of 12 V and anominal capacity of 65 Ah was produced in the same manner as in Example1, except that the organic binder was impregnated in the active materiallayer at the right and left edge portions of the positive electrodeusing the same method as in Example 1, instead of the negativeelectrode. The battery was referred to as Battery B.

COMPARATIVE EXAMPLE 1

[0075] A sealed lead-acid battery with a rated voltage of 12 V and anominal capacity of 65 Ah was produced in the same manner as in Example1, except that the negative electrode did not have the organic binder inthe active material layer at the right and left edge portions thereof.The battery was referred to as Battery C.

COMPARATIVE EXAMPLE 2

[0076] Eleven positive electrodes, which were the same as those inComparative Example 1, respectively sandwiched between in a glass matseparators, which were the same as those in Example 1, were produced.Meanwhile, twelve negative electrodes, which were the same as those inComparative Example 1, respectively encased in bag-shapednon-woven-fabric made of synthetic resin fiber with a thickness of 0.2mm which was subjected to hydrophilicity treatment were produced. Theywere alternately stacked to give an electrode assembly. A sealedlead-acid battery with a rated voltage of 12 V and a nominal capacity of60 Ah was produced in the same manner as in Example 1 using theelectrode assembly. The battery was referred to as Battery D.

[0077] [Evaluation of Batteries]

[0078] Batteries A to D obtained in the above were put through a 1/3 CAdischarge cycle life test at 25%. The discharge was performed at aconstant current of 1/3 CA to 80% of discharge depth. The charge wasperformed at a constant current of 0.2 CA until the battery voltagereached 14.4 V, and after that, at a constant current of 0.05 CA for 4hours. The charge and the discharge were performed alternately. Thebatteries were completely discharged at every 20 cycles. Subsequently,their capacities were checked. FIG. 5 shows the evaluation results.

[0079] As is apparent from FIG. 5, the capacity of Battery C wasremarkably lowered after about 180 cycles and it was below 80% of theinitial discharge capacity after 210 cycles. On the other hand, thecapacities of Batteries A, B and D were over 90% of the initialdischarge capacity even after 800 cycles (Batteries A, B and D had aninitial discharge capacity of 61.0, 60.0 and 56.0 Ah respectively and adischarge capacity after 800 cycles of 55.5, 54.0 and 50.6 Ahrespectively).

[0080] Battery C was disassembled to find that metallic lead depositedon the negative electrode at the side of the electrode assembly and themetallic lead reached the positive electrode, skirting the glass matseparator. This proved that the cause of the remarkable decrease incapacity of Battery C was an internal short circuit.

[0081] Battery A was disassembled in the same manner after 800 cycles.The edges of the electrode assembly were checked to prove that thegrowth of the active material at the right and left edge portions of thenegative electrode similar to the case of Battery C was not found. Theseparation of the active material was found at the right and left edgeportions of the positive electrode; however, the amount of the activematerial separated was small and the separated active material did notextend from the glass mat separator. Presumably, this is because, in thevalve regulated lead-acid battery, the stacking pressure of theelectrode assembly was high and the active material was sufficientlypressed by glass mat separators.

[0082] Battery B was disassembled in the same manner to find thatmetallic lead extended from the right and left edge portions of thenegative electrode, similar to the case of Battery C. However, theorganic binder imparted to the right and left edge portions of thepositive electrode had no conductivity and the binder formed a film onthe surface of the active material. Accordingly, there was no electricalcontact. Additionally, the separation of the active material was notfound at the right and left edge portions of the positive electrode.

EXAMPLE 3

[0083]FIG. 6 shows a transverse sectional view of a relevant part of thelead-acid battery of the present example.

[0084] After a negative electrode 5 was produced in the same manner asin Example 1, a porous resin layer 10 having through holes was formed onthe surface of an active material layer 2 at the right and left edgeportions 4 of the negative electrode 5 by the following process.

[0085] Butyl rubber and styrene rubber were mixed at a weight ratio of97:3. A resin solution was prepared by dissolving 30 parts by weight ofthe obtained mixed resin in 70 parts by weight of toluene. In the resinsolution was dispersed azodicarbonamide as a foaming agent, and theright and left edge portions of the negative electrode 5 wererespectively impregnated with the dispersion. Subsequently, it wasfoamed at 210% and, at the same time, toluene as the solvent was removedtherefrom. During this process, part of the resin component permeatedthe periphery of the surface of the active material layer 2. A porousresin layer 10 with a thickness of 0.05 mm on the surface was formed,and the porous resin layer had a porosity of 55%.

[0086] Using the above-obtained negative electrode and positiveelectrode and glass mat separator which were analogous to those inExample 1, a sealed lead-acid battery with a rated voltage of 12 V and anominal capacity of 65 Ah was obtained in the same manner as inExample 1. The battery was referred to as Battery E.

EXAMPLE 4

[0087] A sealed lead-acid battery with a rated voltage of 12 V and anominal capacity of 65 Ah was obtained in the same manner as in Example3, except that the porous resin layer having through holes was formed onthe surface of the active material at the right and left edge portionsof the positive electrode using the same method as in Example 3, insteadof the negative electrode. The battery was referred to as Battery F.

[0088] Batteries E and F were put through the same cycle life evaluationas in Example 1. FIG. 7 shows the evaluation results. It also shows theresults of Batteries C and D for comparison.

[0089]FIG. 7 indicated that Batteries E and F respectively maintained acapacity of over 90% of the initial discharge capacity even after 800cycles. (Batteries E and F had an initial discharge capacity of 61.0 and60.0 Ah respectively and a discharge capacity after 800 cycles of 55.0and 54.0 Ah respectively). Batteries E and F were disassembled in thesame manner as in Example 1 after 800 cycles to find that Batteries Eand F were in the same condition as Batteries A and B.

[0090] Separately from the cycle evaluation, discharge characteristicsat the initial state were evaluated. FIG. 8 shows the evaluationresults.

[0091]FIG. 8 indicated that Batteries E and F had similar dischargecharacteristics as Battery C and had higher discharge characteristicsthan Battery D. Presumably, this is because the distance betweenelectrodes of Batteries E and F was smaller by the thickness of thenon-woven fabric made of synthetic resin, which reduced the resistanceof electrolyte during discharging.

INDUSTRIAL APPLICABILITY

[0092] As described above, the present invention can provide a lead-acidbattery with longer life by suppressing an internal short circuitresulting from the separation or abnormal growth of an active materialdue to repeated charge/discharge.

[0093] Further, the present invention can provide a lead-acid batterywith longer life and good discharge characteristics, without impairingoutput characteristics, by forming a porous resin layer with throughholes on the surface of an active material layer at the edge portion ofan electrode.

1. A lead-acid battery comprising a positive electrode and a negativeelectrode, each having a current collector comprising an expanded grid,characterized in that at least one of said positive electrode andnegative electrode contains an organic binder in an active materiallayer at an edge portion thereof.
 2. The lead-acid battery in accordancewith claim 1, wherein said organic binder has resistance to acids. 3.The lead-acid battery in accordance with claim 1, wherein said organicbinder has resistance to acids and the ability to form a film.
 4. Thelead-acid battery in accordance with any one of claims 1 to 3, whereinsaid organic binder comprises a resin containing butyl rubber.
 5. Thelead-acid battery in accordance with claim 4, wherein said butyl rubbercontains butyl isocyanate.
 6. The lead-acid battery in accordance withany one of claims 1 to 3, wherein said organic binder comprises butylrubber and styrene rubber.
 7. A lead-acid battery comprising a positiveelectrode and a negative electrode, each having a current collectorcomprising an expanded grid, characterized in that at least one of saidpositive electrode and negative electrode has a porous resin layerformed on the surface of an active material layer at an edge portionthereof.
 8. The lead-acid battery in accordance with claim 7, whereinsaid porous resin layer comprises butyl rubber.
 9. The lead-acid batteryin accordance with claim 8, wherein said butyl rubber contains butylisocyanate.
 10. The lead-acid battery in accordance with claim 7,wherein said porous resin layer comprises butyl rubber and styrenerubber.